Controller for inductive devices



May 10, 1938. D. c. WRIGHT 20,724

CONTROLLER FOR INDUCTIVE DEVICES Original Filed May 19, 1931 INVENTORReissued May 10, 1938 UNITED STATES PATENT OFFICE CONTROLLER FORINDUCTIVE DEVICES Original No. 2,020,670, dated November 12, 1935,

Serial No. 538,472, May 19, 1931.

Application for reissue November 11, 1937, Serial N 0. 174,077

22 Claims.

My invention relates to the control of inductive devices in which it isdesired to reduce the magnetic flux to a minimum when the winding ofrthedevice is deenergized or disconnected from the supply line. Moreparticularly, the invention applies to the control of magnetic clutches,motor field and armature windings and the like, and tolifting magnetsfor handling iron and steel products, such as pig iron, steel ingots,billets,

plates, scrap materials and the like.

It is well known that the opening of a circuit of a highly inductivewinding creates a discharge voltage at the terminals equal to as high asten times the applied voltage. This forms a destructive are on theswitch contacts and introduces a high voltage strain on the insulationof-the winding and the connections thereto. When the cirouit for such awinding is opened the current in the winding reduces to zero almostinstantly but the magnetic flux does not reduce to zero and the deviceenergized by the winding is not completely demagnetized.

If a discharge resistance is used across the terminals of the winding,the unsatisfactory re sults of the high discharge voltage are lessenedbut the magnetic flux decreases slowly and does not reduce to zero. Toreduce the flux quickly, it has been found an advantage to reverse the,voltage applied to the winding, thereby allowing the winding todischarge into the supply line,

and subsequently to reduce the flux to zero by ipermitting a limitedamount of reverse current to flow, thereby completely demagnetizing thewinding. However, as the reverse current continues to flow in thewinding, the magnetic flux will be built up in the opposite directionand will attract the armature or load. If it is left to the judgment ofthe operator to cut off the reverse current, he may cut it off beforethe magnetic flux has reduced to zero, or he may allow the reversecurrent to flow long enough for the flux to build up in the oppositedirection and re-attract the load.

The principal object of my invention is to demagnetize the device bycutting 01f the reverse current in the winding automatically when themagnetic flux produced thereby is zero so that the armature or load willbe released quickly and completely in the event that the load comprisessmall particles of magnetic material.

Another object of the present invention is to obtain rapiddemagnetization of an inductive de vice without creating a highdischarge voltage by setting up reverse voltage connections'before theenergizing circuit is interrupted, and thereafter applying reversevoltage until the magnetic flux has been reduced sufiiciently for themagnet to release its load.

Further objects of the invention are the reducing of the arcing on theswitches or contacts used for energizing and deenergizing the winding,also the saving in electric current and the reduction in the heating ofthe winding.

A further object of the invention is to make adjustable the value ofreverse current allowed to flow in the winding to demagnetize the deviceto the desired extent for different classes of materials and for varioussizes and characteristics of the inductive devices.

For a further understanding of the invention reference is made to theaccompanying drawing, the single figure of which is a schematic diagramrepresenting an embodiment of my invention.

Referring to the drawing, the source of supply is indicated at I and 2,the inductive device or lifting magnet is shown at D with its energizingwinding M, the winding having terminals 3 and 4. The switch forconnecting the winding M to the source of supply for energizing it isshown at S, the switch having an operating coil 5 and the controlcircuit contacts -I I and I2. The switch for reversing the currentthrough the winding M is shown at R with its operating coil 5. Theswitches or contactors S and R are shown as double-pole contactors, butit will be readily understood that two single-pole contactors can beused for either one, each contactor having an operating coil of its own.To limit the reverse current applied to the winding M, resistors l and 8are used, which may be made adjustable to regulate the value of thereverse current in accordance with the electrical and magneticcharacteristics of the device D and the characteristics of the load tobe attracted. The resistors 9 and H! are in the circuit of the operating coil 6 of the contactor R to limit the current in this circuit, andcan be made adjustable to regulate the opening of the contactor R, aslater described. A push button or master switch is shown at P. Thisswitch is preferably of the snap action type which moves quickly fromone position to the other by virtue of a toggle action spring I1 havingone end thereof connected to an arm of the button H, and the other endof which is connected to a stationary point. The arm is movable with theswitch P, and the end of the arm to which the spring is so attached, sothat when the switch is moved over the dead center position from oneposition to the other When it is desired to energize the winding M,

the button N3 of the master switch P is pressed. This opens contacts l5and i6 and closes contacts I3 and E4 to energize the operating coil 5 ofthe contactor S, whereupon the contactor S closes and the winding M isenergized to its fullest extent. Current also flows from the positivesupply through the auxiliary contact Ii, the resistor 9 and through theright hand main contact of the contactor S to the other side of thesource of supply. Another circuit is made from the positive side of theline through the left hand main contact of contactor S, through theresistance Ill and through the auxiliary contact 12 to the negative sideof the line. The resistors 9 and III are of a high value and only a Verysmall current flows. in them in comparison with the amount of currenttaken by the winding M.

When it is desired to demagnetize the device D, push button ll of themaster switch is pressed which opens contacts I3 and I4 and closescontacts I5 and [6. The opening of contacts l3 and i4 deenergizes theoperating coil 5, but before the main contacts of the contactor S havehad time to open, a circuit is closed through the operating coil 6 ofthe contactor R from positive lead I, through the contact II, the wire19, the contacts l5 and 16 of the master switch, the wire 20, theoperating coil 6, the wires 2! and 22 and the contact 12 to the negativesupply lead 2. It is a well known fact that a contactor will close morequickly when its operating winding is energized than it will open whenits operating winding is deenergized. Contactor R therefore closesbefore contactor S opens, thereby providing a discharge circuit for thedevice D from the terminal 4, through the resistor 8, the right handcontact of contactor R, the supply lead I, the supply system to lead 2,the left hand contact of contactor R, and the resistor 7 to the terminal3 of the winding M. Although contacts I! and I2 are opened an instantlater the discharge voltage of the winding M holds the contactor Rclosed by the circuit from the terminal 4, the resistor 9, the contactsl5 and [6, the wire 20, the operating coil 6, the wire 2| and theresistor III to the terminal 3 of the winding M. The discharge voltageof the magnet is now opposed to the supply line voltage and when thedischarge voltage, which may be twice or three times as much as thesupply voltage at the beginning of the discharge, has reduced to a valueequal and opposed to line voltage, then the current in the winding M iszero. Current now begins to flow in the reverse direction through thewinding from positive lead I through the right hand contact of contactorR, the resistor 8, the winding M, the resistor l and the left handcontact of contactor R to the negative supply lead 2. The current nowbegins to build up in the reverse direction in the magnet and causes theremaining flux to be decreased to a zero value, at which time thedischarge voltage will be approximately zero and the operating coil 6will be sufficiently deenergized to permit the contactor R to open,thereby cutting off the reverse current at the moment the device D iscompletely demagnetized.

It is apparent from the foregoing description that during the workingperiod of the magnet, the winding is never disconnected entirely fromthe source of supply but is connected either through switches S or R, orboth,'so that a discharge circuit through the source of supply isprovided at all times.

In commercial lifting magnets of large size, it has been found that theopening of contactor R is approximately 1%; seconds after the opening ofcontactor S. The same controller can be used for different sizes ofmagnets for inductive windings by adjusting the resistors 9 and 10, sothat the contactor R drops out at the time the load is released from themagnet, thereby preventing the reverse current building up to such avalue that the magnetic flux will be reversed, causing the magnet tore-attract its load. The closing of contactor R before the opening ofthe contactor S, connects a discharge path for the winding before it isdisconnected from the source of supply by the contactor S, therebyreducing the arcing at the main contacts of S to a very small amount.This operation also reduces the discharge voltage on the magnet to aboutone-third of the value experienced if the contactor S is opened first.

In one installation of this invention with a 230 volt supply line, itwas found that as a. result of the reversal of the current in the magnetD before the energizing switch S had opened, the discharge voltage ofthe magnet D reached only about 1100 volts, whereas without this rapidreversal it was observed to reach approximately 3500 volts. With thedischarge voltage reduced to 230 volts, the current in the magneticwinding became zero. However, the voltage in. the magnet did not reachzero until the reverse current had built up to 8 or 9 amperes, which wasthe proper value for opening the contactor R to cut off the reversecurrent. The voltage on the operating coil 6 was at the time thecontactor opened about 27 volts which would be about the voltage acrossthe terminals of the magnet winding M at the time the contactor R startsto open, but the time delay of the contactor in opena ing allowed themagnet voltage to be practically zero when the contactors opened andinterrupted the reverse current.

Experiments made with different kinds of magnetic materials indicatethat the magnet drops its load quickly and cleanly when the voltage onthe magnet is zero, which corresponds to the zero condition of flux inthe magneticcircuit of the magnet. This is a desired condition when themagnet is handling small pieces of scrap material. If the magnet ishandling heavy ingots, the ingots would drop off due to the weightbefore the flux reaches zero, so that for commercial purposes it isadvisable to adjust the resistors 9 and H! at arbitrary values to secureclean dropping of the load of any class of materials to be handled. Ifthe same control device is to be used on large and small magnets, it isadvisable to change the resistors 9 and H! to give the best results.

I claim:

1. An apparatus for controlling the operation of a lifting magnet,comprising means for energizing the magnet to lift a load, meansoperable to render said first mentioned means ineffective and todeenergize the magnet and drop. the load, switching means for setting upreverse electro motive-force connections for said magnet before saiddeenergizing means becomes effective, said switching means beingrendered operative to apply reverse electromotive-force to the magnetupon the operation of said second mentioned means, and means controlledby the magnet for opening the switch to cut off the reverseelectromotiveforce when the magnet is deenergized sufiicient- 1y to dropits load.

2. Incombination, a lifting magnet, means for energizing the magnet byapplying a voltage to the magnet, means for deenergizing the magnet,said deenergizing means comprising a magnetically operated switch tocause the polarity of the voltage applied to the magnet to be reversedand to permit reversal of current in .said magnet, manual means forcausing said switch to become closed to permit the polarity of thevoltageapplied to the magnet to be reversed, and means controlled by themagnetic flux in, said magnet for causing said magnetically operatedswitch to remain momentarily closed while said voltage of reversepolarity and said reverse current are eifective until magnetic flux hasreached a value which will cause the magnet to drop its load.

3. An apparatus for controlling the inductive winding, comprising aswitch for admitting an energizing current to the winding to produce amagnetic flux, 3, second switch for setting up reverse currentconnections to thewinding, and magnetically operated means for causingopening of said first mentioned switch and for causing closing of saidsecond mentioned switch to set up said reverse current connectionsbefore opening of said first mentioned switch, to interrupt theenergizing current, said second switch admitting the reverse current toneutralize the induced flux after said induced flux has decreasedapredetermined amount. 7

4. An apparatus for controlling an inductive winding, comprising ,asource of current supply, a magnetically-dperated switch for admittingcurrent to the winding to energize the same, a secondmagnetically-operated switch for reversing the applied polarity of saidcurrent supply and for admitting reverse current to the winding toneutralize the induced flux therein, a relay circuit for said firstmentioned magneticallyoperated switch and a relay circuit for saidsecond mentioned magnetically-operated switch, and simultaneouslyoperable means for causing said second mentioned magnetically-operatedswitch to become closed to set up connections for reversing the appliedpolarity of said current supply before causing said first mentionedmagnetically-operated switch to become open to interrupt the energizingcurrent through said winding, and means operable by the induced flux insaid winding for maintaining said second mentioned magnetically-operatedswitch closed until the flux in said winding has reached a predeterminedminimum.

5. The combination with an inductive winding, 9. source of power, tworesistors, a pair of contacts, a circuit connecting the contacts andwinding in series to said source, of means for connecting each of saidresistors in parallel with the winding, and means for opening saidcontacts whereby the winding remains connected to said source in serieswith said resistors so that the flow of current in the winding isreversed.

6. The combination with an inductive winding, a source of power, tworesistors, a pair of contacts, a circuit connecting the contacts andwinding in series to said source, of means for connecting each of saidresistors in parallel with the winding, means for opening said contactswhereby the winding remains connected to said source in series with saidresistors so that the fiow of current in the winding is reversed, andmeans controlled by fiux produced in the winding for disconnecting thewinding from said source.

7. The combination with an inductive winding, 9. source of power, tworesistors, of means for connecting the winding to said source so that isconnected in series with the resistors to the source so that currentflows through the winding in adirection opposite to said givendirection.

8'. The combination with an inductive winding, a source of power,current limiting resistance and contacts for connecting the winding tosaid source, of contacting means for connecting the resistance to thesource in series with said contacts, and means whereby the opening ofsaid contacts leaves the winding connected to the source in series withthe resistance and with the qpolarityof the source reversed with respectto the winding.

9. The combination with an inductive winding, a source of power and tworesistors, of contacting means for connecting the winding to the saidsource, means for connecting each of said resistors in parallel with thewinding and in series with said contacting means, and means whereby theopening of said contacting means leaves the winding connected to saidsource in series with each of said resistors.

10. In combination, a source of power, an inductive winding connected tosaid source at all times during the working period of the winding, meansfor reversing the current in the winding during said period, and meansresponsive to the electrical condition of the winding to cut oif thereverse current and thereby terminate the working period.

11. In combination, a source of power, an inductive winding connected tosaid source at all times during the working period of the winding, meansfor reversing the current in the winding .during said period, wherebythe normal discharge voltage at the terminals of the winding is reduced,and means controlled by the discharge voltage to discontinue the flow ofsaid reverse current.

12. In combination, a source of supply, a translating device, aresistance, contacting means for connecting said device to the source sothat current flows through the device in one direction, contacting meansfor connecting the device to the source in series with said resistancewith the polarity reversed, means for closing the second contactingmeans while current flows through the device and the first contactingmeans, and means for opening the first contacting means, leaving thedevice connected to the source through the second contacting means.

13. In combination, a source of supply, a translating device,resistance, contacting means for connecting said device to the source sothat current flows through the device in one direction, contacting meansfor connecting the device to the source in series with said resistance,with the polarity reversed, means for closing the second contactingmeans while current flows through the device and the first contactingmeans, means for opening the first contacting means, leaving the deviceconnected to the source through the second contacting means, and meanscontrolled by the electrical condition of said device for opening thesaid second contacting means.

14. In combination, a magnet, a winding therefor, a source of power, acircuit for connecting said winding to said source of power, anelectroresponsive contactor operable to open and close said circuit, asecond circuit for connecting said winding to the source of power toeffect reversal ofthe current flow through the winding, an electro-responsive contactor operable to open and close said second circuit,means for actuating said contactors and being operable to actuate thecontactor in the second circuit to close said second circuit before thecurrent in the first circuit is interrupted by the contactor in saidcircuit.

15. In combination, a magnet, a winding therefor, a source of power, acircuit for connecting said winding to said source of power, anelectroresponsive contactor operable to open and close said circuit, asecond circuit for connecting said winding to the source of power toeffect reversal of the current flow through the winding, anelectro-responsive contactor operable to open and close said secondcircuit, means for actuating said contactors and being operable toactuate the contactor in the second circuit to close said sec- ;ondcircuit before the current in the first circuit is interrupted by thecontactor in said. circuit, said second contactor being responsive tothe electrical condition of the winding and being operably responsive tovariations in the electrical condition of the winding to interrupt saidsecond circuit.

16. A system for energizing and deenergizing a winding, comprising meansoperable to close and to open a first circuit for controlling theapplication of electromotive-force to said winding in a predetermineddirection, means operable to complete a second circuit for applyingelectromotiveforce to said winding in a direction opposite to saidpredetermined direction, said means operating to close said secondcircuit before said first mentioned means operates to open said firstcircuit, and means responsive to the electromotiveforce across saidwinding for controlling the duration of application of saidelectromotive-force in said opposite direction.

17. A system for energizing and deenergizing a winding, comprising meansoperable to close and to open a first circuit for controlling theapplication of electromotive-force to said winding in a predetermineddirection, means operable to complete a second circuit for applyingelectromotive-force to said winding in a direction opposite to saidpredetermined direction, said means operating to close said secondcircuit before said first mentioned means operates to open said firstcircuit, and means for automatically controlling the duration ofapplication of said electromotiveforce in said opposite direction.

18. A system for energizing and deenergizing a winding, comprising meansoperable to close and to open a first circuit for controlling theapplication of electromotive-force to said winding in a predetermineddirection, means operable to complete a second circuit for applyingelectro- ,motive-force to said winding inv a direction opposite to saidpredetermined direction, said means operating'to close said secondcircuit before said first mentioned means operates to open said firstcircuit, and means, responsive to the electromotive force across saidwinding, for maintaining said second circuit closed after said firstcircuit opens and for automatically controlling the duration ofapplication of said electromotive-force in said opposite direction.

19. A system for energizing and deenergizing a magnet, comprising meansoperable to close and to open a first circuit for controlling theapplication of electromotive-force to said magnet in a predetermineddirection, means operable to complete a second circuit for applyingelectromotive-force to said magnet in a direction opposite to saidpredetermined direction, said means operating to close said secondcircuit before said first mentioned means operates to open said firstcrcuit, and means responsive to the electromotiveforce across saidmagnet for controlling the duration of application of saidelectromotive-force in said opposite direction, to thereby preventproduction of magnetic flux by said magnet in a direction reversed tothat produced when it is in said first circuit.

20. A system for energizing and deenergizing a winding, comprising meansoperable to close and to open a first circuit for controlling theapplication of electromotive-force to said winding in a predetermineddirection, and means operable to complete a second circuit for applyingelectromotive-force to said winding in a direction opposite to saidpredetermined direction, said means operating to close said secondcircuit before said first mentioned means operates to open said firstcircuit.

21. A method of demagnetizing a magnet connected to a source of power,which comprises applying electromotive-force to saidmagnet in adirection opposed to the electromotive-force applied by said source ofpower before said magnet is disconnected from said source of power, andthen removing said opposed electromotive-force when said magnet issubstantially completely demagnetized.

22. A method of demagnetizing a magnet connected to a source of power,which comprises applying electromotive force to said magnet in adirection opposed to the electromotive-force ap'' plied by said sourceof power before said magnet is disconnected from said source of power.

DAVID C. WRIGHT.

